Hydrogen-based fuel cells are becoming increasingly popular as an alternative to crude oil-based internal combustion engines. Specifically, hydrogen can be converted to electricity through the use of a H2—O2 fuel cell. The by-product of this type of a fuel cell is water, making this a “green” or environmentally friendly technology. At the heart of the fuel cell is the proton exchange membrane (PEM), which transports protons from the anode to the cathode while providing electronic insulation between them. There are many types of electrolyte materials, each with specific limitations. Generally, such materials either have too low a proton mobility or don't operate at a high enough temperature to be useful in fuel cells.
Some of the most popular electrolyte materials are polymer exchange membranes, phosphoric acid membranes, and solid oxide membranes. Polymer exchange membranes, or more specifically solid organic polymer poly-perfluorosulfonic acids such as Nafion™, require hydration. However, this limits their operation to temperatures below 100° C., thus requiring the use of expensive noble metal catalysts such as platinum. These electrolytes also suffer from fuel cross-over due to their porous hydrated nature. Phosphoric acid membranes are typically operated from 150° C. to 200° C. Being a liquid electrolyte, these membranes suffer from membrane leakage and fuel cross-over problems. They also require the use of expensive platinum catalysts. Solid oxide membranes are typically operated between 700° C. to 1000° C., where the use of platinum as an electrode material can be reduced. This temperature range is used to achieve the desired oxide anion conductivity. These membranes being solid in nature do not suffer from fuel cross-over problems. With these current fuel cell membrane materials, however, there remains a temperature region between about 100° C. and 700° C. that currently no one membrane can provide for optimum performance. In this temperature range, anhydrous proton conductors are desirable.
Thus, what is needed are new compounds for use in proton exchange membranes which are able to operate in a wide variety of temperature ranges, including in the intermediate temperature range of about 100° C. to 700° C., and new and improved methods of making these compounds.